#include <cmath>
#include <cstdio>
#include <vector>
#include <iostream>
#include <algorithm>
using namespace std;


int main() {
    int p,d,m,s;
    cin>>p>>d>>m>>s;
    int sum=0,ans=0;
    int x=(p-m)/d;
    for(int i=0;i<=x;i++){
        sum+=p;
        ans++;
        p-=d;
        if(sum>s){
            ans--;
            break;
        }
        else if(sum==s){
            break;
        }
        //cout<<sum<<endl;
        //cout<<"p= "<<p<<endl;
    }
    if(sum>=s){
        cout<<ans;
        return 0;
    }
    p=m;
    //cout<<"p= "<<p<<" sum= "<<sum<<endl;
    for(int i=1;;i++){
        sum+=p;
        ans++;
        if(sum>s){
            ans--;
            break;
        }
        else if(sum==s){
            break;
        }
        //cout<<"REs= "<<sum<<' '<<ans<<endl;
    }
    cout<<ans<<endl;
    /* Enter your code here. Read input from STDIN. Print output to STDOUT */   
    return 0;
}